The argument is that “thank you” and “obrigado” and “merci” are all ways of saying “I am in your debt”, which is a way of stating a position of inferiority. Saying “my pleasure” is saying “why no, you couldn’t be in debt to me because I did it for my own pleasure”. Saying “no problem” is saying “It cost me nothing to do that, so your debt is likewise nothing”. I don’t know if I believe this, mind you. But I’ll remember it every time I get a flash of “no problem” annoyance.
